The Effects of Multiphase Formation on Strain Relaxation and Magnetization in Multiferroic BiFeO3 Thin Films


  • This work was supported by NSF MRSEC DMR-00-0520471, ONR N000140110761, ONR N000140410085, NSF DMR 0094265 (CAREER), NSF DMR 0231291 and NSF 0095166. It was also supported by W. M. Keck Foundation and Provincia Autonoma di Trento, Italy, under the Microcombi project. We acknowledge the use of the TEMs in the Nanoscale Imaging Spectroscopy and Properties (NISP) laboratory at the University of Maryland. The NISP laboratory is a Shared Experimental Facility of our NSF MRSEC.


Multiferroic epitaxial Bi-Fe-O thin films of different thicknesses (15–500 nm) were grown on SrTiO3 (001) substrates by pulsed laser deposition under various oxygen partial pressures to investigate the microstructural evolution in the Bi-Fe-O system and its effect on misfit strain relaxation and on the magnetic properties of the films. Films grown at low oxygen partial pressure show the canted antiferromagnetic phase α-Fe2O3 embedded in a matrix of BiFeO3. The ferromagnetic phase, γ-Fe2O3 is found to precipitate inside the α-Fe2O3 grains. The formation of these phases changes the magnetic properties of the films and the misfit strain relaxation mechanism. The multiphase films exhibit both highly strained and fully relaxed BiFeO3 regions in the same film. The magnetization in the multiphase Bi-Fe-O films is controlled by the presence of the γ-Fe2O3 phase rather than heteroepitaxial strain as it is the case in pure single phase BiFeO3. Also, our results show that this unique accommodation of misfit strain by the formation of α-Fe2O3 gives rise to significant enhancement of the piezo electric properties of BiFeO3.